The auto is a good idea, a lot more flexibility in the Freelander - the red 3 door that was for sale recently would have been a good car to build from. I'm not sure which of the V6 or TD4 is most likely to expire when you're 50kms from tar seal or up to the doors in water. The TD4 is more reliable on road - but which is more likely to suffer problems on low crawling revs for long periods and getting wet?
The G4 Challenge FLs were often V6s but a couple of TD4s were used iirc.
I think the TD4 would be my choice for off road use. It has better low speed torque and doesn't mind low RPM use so much. The V6 is very reliant on its cooling fans when just crawling along. Electric cooling fans don't like to hit water, if they are running at max chat!!